When granular lading, such as bauxite, bentonite, cement, flour, and the like is loaded into a railway hopper car having a hopper outlet closed by a sliding gate, a substantial part of the lading escapes between the hopper outlet chute and the gate until sufficient lading has been retained on the gate to close off the leakage spaces.
Additionally, in order to supply air to operate diesel locomotives in relatively long tunnels, it is customary to pressurize the tunnels. When railway cars containing lading are drawn through such tunnels, the hopper compartments become pressurized and retain the pressure on emerging from the tunnel. This pressure serves to discharge some of the lading through the leakage space between the hopper chutes and the gates. The discharged lading not only represents a loss in transported materials, but also contaminates the railway roadbed so that it must be periodically removed.
The prior art is prolific in the design of seals which have been applied to such sliding gates in an effort to minimize waste of lading caused by such pressurized conditions, and losses caused by the inevitable mechanical distortion in the components used to effect such seals. Railway hopper cars are subjected to extremely severe operating conditions, and additionally, the personnel opening and closing such gates in many instances employ force and means which cause any seals dependent upon friction or tight contact to open.
Generally speaking, all of the prior art sealing arrangements attempt to employ mechanical elements, either rigid or resilient, to effect a tight friction contact seal between the relative moving slide gate and the adjacent hopper chute frame defining the hopper opening. Inevitably, due to the relatively large size of hopper car gates and the severe usage and treatment to which these gates are subjected, one or more elements of the seals become distorted and consequently the integrity of the seal is impaired to the point that lading is unnecessarily discharged. The resulting waste, of course, represents an expensive loss, as well as a discharged contaminant as far as the railway bed is concerned.